Lubricating grease and process of manufacture



Patented Sept. 16, 1952 LUBRICATING GREASE AND PROCESS A OF MANUFACTURE7 Arnold J. Morway,

Clark Township,

Union County, N. J., assignor to Standard Oil Devel-. opment Company, acorporation of Delaware No Drawing. Application June 24, 1950, f

Serial No. 170,247

14 Claims. (Cl. 252-41) The present invention relates to an improvedlubricating grease and a process for its manufacture. The invention isparticularly concerned with improvements in the process of preparinggreases, and in a combination of ingredients used in such processes,resulting in products having better lubrication life, improved oxidationresistance and lower volatility.

It has previously been suggested that the high temperature performanceof lubricating greases subjected to severe operating conditions,particularly where long life and sustained operation at elevatedtemperatures are required, may be improved by adding to the soapthickener various constituents of relatively low molecular Weight.According to some authorities, these materials, namely the low molecularweight salts and the conventional metal soaps of long chain fatty acids,combine to form a complex which has the property of thickeninglubricating oils to grease consistency and also imparting a high degreeof mechanical and thermal stability. vThus, it has been suggested thatcombinations of conventional sodium, calcium and other metal soaps withsalts of the same or related metals, such as the acesoap separation thanthe parafiinic oils. It is simpler to make highly stable soapsuspensions with these non-paraffinic, low viscosity'index oils. Forpurposes of the present invention, it ispreferred to use lubricatingoils of viscosity index to 60, viscosity at 100 F. of -0 to 1500's. S.U.,

tates, nitrates, acrylates, furoates, and the like,

may be used for this purpose.

According to the present invention, still further improvements may bemade in greases of the combined salt-soap complex type by the method ofcompounding and by selection of the lubricating' oil constituents and bysuitable choice and control of the conditions under which the soap andsalt are addedthereto. p

Most commercial lubricating greases are prepared from mineral baselubricating oils thicking oil range having a fairly large so-calledaromatic or naphthenic content. Such oils have a comparatively lowviscosity index. The reason for this preference is that the naphthenicor aromatic oils, that is,. low A. P. I. gravity oils such as Gulf Coastoils and other asphaltic crudes and containing a substantial percent ofnon-paraffinic ingredients, are much better solvents and dispersants forsoaps than are the paraffinic oils.

Grease prepared from these give less trouble with preferably/at least300 or higher, and flash points of 280 to 480, F., preferably 340 to 440F.

On the other hand, it is well-known inthe lubricating industry that theparafilnic type oils, obtained either from parafiinic crudes directly orby solvent extraction of mixed or asphaltic base crudes, have markedlysuperior viscosity indexes. For this reason, thehighly paraffinic oilswould be preferable if they could be compoundedsatisfactorily intogreases. I Another disadvantage of the conventional naphthenic oraromatic type oils is that they are relatively volatile for a givenviscosity. Non-parafiinicoils of a given viscosity usually have a lowerflash point than para ffinic oils of similar viscosity. The non-viscousnaphthenic oils tend to flash at or evenbelow grease cookingtemperatures. Also, for high temperature lubrication, it has beenconsidered necessary in the past to use oils ofrelatively very highviscosity in order to avoid undue volatility. At the same time, it hasbeen necessary to use large quantities of soap to obtain a given greasecon-'- sistency because of the higher soap solvency of the oil.

Since the parafiinic oils, on the other hand, have a very much lowervolatility for the same viscosity, it would appear desirable tosubstitute them. However, as indicatedabove, they have notbeen. usedextensively in grease manufacture because ofthe difliculty ofobtaining'satisfact'ory soap dispersion and grease texture.

' The paramnic'oils are superior to the naphthenic crude products intheir resistance to oxidation. Whilenaphthenic oils can be stabilizedquite efiectively by the proper use of oxidation inhibitors, they arestill subject to greater oxidative deterioration than the paraffinicoils. Even the latter can, of course be improved by the use of goodinhibitors.

According to the present invention, lubricating grea'ses of thesalt-soap thickened type may be prepared with especially desirableproperties for high temperature performance by first forming a soap-salt concentrate in a relatively viscous aromatic type oil. As notedabove, such an oil should preferably have a viscosity of 250 to 1500 S.S. U. at 100 F., the higher ranges being preferred. Thereafter, asubstantial quantity of a substantially paraffinic oil is blended intothe soap-salt concentrate at continued grease cooking temperatures, e.g. 280 to 450 F., preferably 300 to 350 F., and a stable grease of goodhigh temperature properties, suitable for long life lubrication, is thusprepared.

It is possible to use oils having a moderately good viscosity index,even for this first fraction. Oils derived from certain Panhandle orMid- Continent crudes, or those obtained from semiparaflinic stocks, oronly partially refined by reduced solvent treatment, etc., may beemployed.

The introduction of paraflinic oil into a preformed grease is not merelya matter of blending. While some types of mineral lubricating oils maybe worked into soap concentrates successfully when cold, the highlyparaflinic oils, which are particularly desirable because of their highviscosity indexes and decreased volatility, do not combine with theconcentrates to form stable greases. They are subject to soapseparation, particularly when subjected to heating and cooling as inhigh temp. service. They also tend to separate soap from oil in storageat ordinary temperatures. According to the present invention, however,if the paraflinic oils are added very gradually, and. at the cookingtemperatures which are usually available in standard steam heated greasekettles and worked mechanically while being stirred into the preformedthick grease or soap-salt concentrate, greases of good structurestability maybe prepared. For this purpose, paraflinic oils of 90 to 120viscosity index, with viscosities of about 200 to 500 S. S. U. at 100F., and with flash points of 300 to 500 F., preferably 440 to 480 F.,are preferred.

Another feature of the present invention is the discovery that thedispersion of the soap-salt thickener, which largely determines thestructural stability of the grease, may be greatly improved by drasticmechanical homogenization, e. g., in a drastic homogenizer of theManton- Gaulin type. Alternatively, the grease may be milled in a, paintmill, or the like, with quite satisfactory results.

The invention will be more fully understood by reference to the examplesbelow. In general, however, about 2 to 20 parts by weight of suitablefatty acids of the C12 to C24 range, preferably saturated orsubstantially so, are first combined at ambient temperatures with about20 to 50 parts by weight of the aromatic or :naphtheni'c (or mixed base)type mineral oil of relatively high viscosity. About 1 to 15 parts byweight of the other soap-salt constituent, e. g.,

'a low molecular weight carboxylic acid or an aldehyde capable ofundergoing the Cannizzaro reaction to form such an acid, is added tothis mixture along with a sufficient quantity of a metal base tosaponify the fatty acids and to combine with the acid or to undergo theCannizzaro reaction with the aldehyde where an acid-forming aldehyde,such as furfural, benzaldehyde, formaldehyde, or the like, is used.

The mixture of ingredients describedabove is heated tosoap-cookingtemperature, normally between about 300 and 350 F. until thereactions are substantially complete and the water resulting therefromhas been substantially or completely evaporated. Oil refinery equipmentis often heated with steam at available pressure and temperature,usually around 125 p. s. i. g. and 340 F. Where the Cannizzaro reactionis taking place, e. g., where an aldehyde such as furfural or thiopheneis being used, alcohols resulting therefrom should be substantiallyremoved. In some cases, minor proportions of such alcohols may bepermitted to remain in the grease, as is now known in the art.

The foregoing process results in a soap or soap-salt concentrate inrelatively viscous aromatic or other non-paraffinic type oil which hasrelatively good solvent properties for the soap constituent. Withoutsubstantially lowering the temperature, 25 to 50 parts by weight of arelatively lower viscosity paraifinic oil (of higher A. P. I. gravity,higher flash point, and higher viscosity index, relative to itsviscosity) are blended in gradually, heat being applied to keep up thetemperature and stirring being continued throughout the blending. Thisprocess produces a good product which may be further improved in textureand mechanical stability by extensive homogenization or mechanicalmilling, as suggested above.

Example I A composition of the following ingredients was prepared in thegeneral manner described above.

The Hydrofol acids (substantially saturated) and the naphthenic typemineral oil were charged to a steam heated grease kettle and mixedwithout heating. A 33 aqueous solution of sodium hydroxide was added andthe acids neutralized. The furfural was then added and by a Cannizzaroreaction it was reacted with the excess sodium hydroxide used, over andabove that required for the neutralization of the Hydrofol acids.Heating was then initiated, and the mass was dehydrated andsubstantially de-alcoholized. The resulting soap-salt complex was thusdispersed in the high viscosity naphthenic type mineral oil to form athick grease or soap concentrate. The concentrate was heated to 320-340F. (highest temperature obtainable with usually available steampressures). After cooking for approximately one hour, the low viscosityparaffinic type oil was slowly added to the hot soap dispersion, cookingand stirring being continued. When this oil was completely added, thephenyl alpha naphthylamine wasadded to inhibit oxidation. Thereafter,the grease was cooled to about F. while agitating, by releasing thesteam and running cold water through the kettle jacket. Then the greaseproduct was semi-fluid; it could be poured slowly at room temperature.Homogenizing the grease by passing through a paint mill or Manton-Gaulintype homogenizer thickened it very substantially to a solid smoothgrease structure. This product showed no flow It showed the Worked 60strokes 321 Worked 60,000 strokes 356 Dropping point, "F j 500+ ExampleII Ingredients ggg gg "Hydrofol Acids 5a" 15.00 Close cut Coastal typemineral oil 300 S. U. S. V's/100 12,350" F. Flash point 30. Furiural 10.00 Sodium hydroxide 15. 00 Paraflinic type mineral oil of 250 S 460 F.Flash point v a9. 00 Phenyl alpha naphthylamine l. 00

Prepared in similar manner to Example I. I I Penetrations mm./ 10:

Unworked 214 Worked 60 strokes 242 Worked 60,000 352 strokes. Droppingpoint, F .500+ I Norma Hoffman bomb 700 hours no drop in oxidation.oxygen pressure. Lubrication life 1300 10,000 R. P. M. spindle g test at300 F. hours.

Example III:

Ingredients 7 giggfiz Oleic acid I v 7.5 "Hydrofol Acids 53 7.Naphthenic mineral 01, 1200 S S Example I Sodium hydroxide 51oParafitlnic oil of 150 S. U. S. VlS. at 100 F., as in Example I. 34. 5Phenyl alpha naphthylamine l. 0

Prepared in similar manner to Example I.

Since the temperature of 330 F. was the maximum obtainable in thisparticular steam kettle, the grease was then transferred to a fireheated kettle and heated to 400 F. The grease drawn at 330F.wassemi-fluid and further homogenization did not materially thicken it. Thegrease cooked to 400 F. was substantially harder.

Grease from steam kettle after homogenization: Penetration mm./ 3Dropping point "F 500+ Grease heated to 400 F.: Penetration The Hydrofolacids and the aromatic mineral oil were charged to a steam heated greasekettle and heated to 150 F. The acetic acid was then added and bothacids were co-neutralized with the sodium hydroxide (40% aqueoussolution).

Appearance-Slightly roughsmooths out on homogenization Penetrationunworked 131 Penetrationworked 60 strokes 147 Comparison of greases-(volatility andspind le'l ife) 10,000 R; P. M. Spindle Test at 300 F,Hours Percent Volatility 1 ExampleII 1300 Similar greaseof sameviscosity min eral oil but containing all aromatic type oil. (Average of3 greases -B l%rcentloss;from packed bearing held 500 hours in an ovenat l The greasein this high speed spindle bearing was found, to berather heavy probably from evaporation of the more volatile. oilconstituentsg'but no oil was found condensed in the quill.Lubricationwas'continuously satisiactory.., j

I This grease residue was dry and powdery and a large amount of oil wasfound condensed in the quill. Lubrication had failed. V

What is-claimed is:

1. The rocess of making a stable high temperature lubricating greasewhich comprises combining 2 to 20 parts by weight of fatty acid of theC12 to C24 range with 20 to 50 parts ofan aromatic type mineral baselubricating oil of relatively high viscosity, adding 1 to 15 parts oforganic material having-a molecular weight below about selected from thegroup consisting of carboxylic acids and aldehydes undergoing theCannizzaro reaction and a sufficientamount of a metal base selected fromthe group consisting of alkali metal and alkaline earth metal bases toform a soapsalt complex with said fatty acid and said organic material,heating the aforesaid ingredients with stirring to a soap-cookingtemperature for a period of time to substantially complete saidsoap-salt reaction, and thereafter gradually adding and blending in 25to 50 parts of a relatively low viscosity and low volatility minerallubricating oil of paraffinie type while applying heat. the amount ofsaid paraflinic-type oil being not substantially smaller than that ofsaid aromatic-type oil and substantially maintaining a cookingtemperature between about 280 F. and 450 F. to form a grease ofrelatively high viscosity index and relatively low volatility.

2. The process of preparing a stable lubricating grease of relativelyhigh viscosity index and relatively low viscosity, which comprisescombining about 2 to 20 parts by weight of substantially saturated fattyacid of the C12 to C24 range with about 20 to 50 parts of a relativelyviscous aromatic mineral base lubricating oil at substantially ambienttemperatures, adding an excess of an alkali metal base saponifyingagent, adding 1 to 15 parts of an organic aldehyde of molecular weightbelow about 160 capable of undergoing the Cannizzaro reaction with saidbase, beating and stirring to a grease cooking temperature of about 300to 350 F. for a period of time to substantially convert said fatty acidand said aldehyde into a soap and salt mixture concentrate in said oil,thereafter substantially maintaining said cooking temperature betweenabout 300 and 350 F. and graduallystirringin about 25 to 50 parts ofsubstantially parafiinic type lubricating oil of viscosity substantiallylower than said aromatic type-oil; cooling the grease and subjecting itto drastic mechanical working to homogenize it.

.3. Process according toclaim 1 wherein said organicunaterial isfurfural. 4. Process according to claim 1 wherein said fatty acid issubstantially saturated.

5. Process according to claim 2 wherein said alkali metal base is NaOH.7

6. Process according to claim 2 wherein said aldehyde is furfural.

7. Process according to claim 1 wherein said organicmaterial isacarboxylic acid of 2 to 7 carbon atoms.

8. Process according to claim 1 wherein said organic material is, analiphatic carboxylic acid of 2 to 4 carbon atoms.

9. A structurally stable lubricating grease composition consistingessentially of about 20 to 50 parts by weight of a relatively viscousnon-parafllnic type mineral lubricating oil of relatively low viscosityindex, 25 to 50 parts of a relatively less'viscous paraflinic typemineral lubricating oil, the amount of paraifim'c-type oil being notsubstantially smaller than that of said non-paraffinic oil, said oilsbeing thickened to a grease consistency with a combination of about 2 to22 parts of a metal selected from the group consisting of alkali andalkaline earth metals and metal soap of fatty acid of the C12 to C24range and about 2 to 20 parts of the salt of the same metal andcarboxylic acid of less than 8 carbon atoms-and molecularweight belowabout 160, said grease being stabilized structurally by sustainedcooking of the blendof nonparaff1nic oil and soap at a temperaturebetween 280and 450 F., while said paraifinie oil is gradually blendedtherein.

- 10.Composition according to'claim 9 wherein 40 12. Compositionaccording to claim 9 character ized by an extremely fine dispersion ofsalt-soap thickener as obtained by severe mechanical homogenization ofthecold final blend.

13. Process according to claim 1 wherein said grease is cooled andthereafter mechanically milled to give it a solid consistency.

14. A solid milled structurally stable lubricating grease of thesalt-soap complex type, comprising substantial proportions of relativelyparaffinic high viscosity index mineral oil of low viscosity and notsubstantially more than equal proportions of relatively non-parafliniclow viscosity index mineral oil of relatively high viscosity and agrease forming proportion of sodium soap of substantially saturatedfatty acids of the C12 to C24 range combined with sodium salt ofcarboxylic acid of molecular weight below 160, said grease beingstabilized structurally by sustained cooking of the blend ofnon-parafiinic oil and soap at a temperature between 280 and 450 F.,while said paraffinic oil is gradually blended therein.

ARNOLD J. MORWAY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES Page 435 of the book by Klemgardentitled Lubricating Greases (1937)

1. THE PROCESS OF MAKING A STABLE HIGH TEMPERATURE LUBRICATING GREASEWHICH COMPRISES COMBINING 3 TO 20 PARTS BY WEIGHT OF FATTY ACID OF THEC12 TO C24 RANGE WITH 30 TO 50 PARTS OF AN AROMATIC TYPE MINERAL BASELUBRICATING OIL OF RELATIVELY HIGH VISCOSITY, ADDING 1 TO 15 PARTS OFORGANIC MATERIAL HAVING A MOLECULAR WEIGHT BELOW ABOUT 160 SELECTED FROMTHE GROUP CONSISTING OF CARBOXYLIC ACIDS AND ALDEHYDES UNDERGOING THECANNIZZARO REACTION AND A SUFFICIENT AMOUNT OF A METAL BASE SELECTEDFROM THE GROUP CONSISTING OF ALKALI METAL AND ALKALINE EARTH METAL BASESTO FORM A SOAPSALT COMPLEX WITH SAID FATTY ACID AND SAID ORGANICMATERIAL, HEATING THE AFORESAID INGREDIENTS WITH STIRRING TO ASOAP-COOKING TEMPERATURE FOR A PERIOD OF TIME TO SUBSTANTIALLY COMPLETESAID SOAP-SALT REACTION, AND THEREAFTER GRADULLY ADDING SAID BLENDING IN25 TO 50 PARTS OF A RELATIVELY LOW VISCOSITY AND LOW VOLATILITY MINERALLUBRICATING OIL OF PARAFFINIC TYPE WHILE APPLYING HEAT, THE AMOUNT OFSAID PARAFFINIC-TYPE OIL BEING NOT SUBSTANTIALLY SMALLER THAN THAT OFSAID AROMATIC-TYPE OIL AND SUBSTANTIALLY MAINTAINING A COOKINGTEMPERATURE BETWEEN ABOUT 280* F. AND 450* F. TO FORM A GREASE OFRELATIVELY HIGH VISCOSITY INDEX AND RELATIVELY LOW VOLATILITY.